1. Field of the Invention
The present invention relates generally to an apparatus and method for delivering fuel for combustion in an internal combustion engine. More specifically, the present invention relates to an apparatus and method for increasing the speed of a fuel injector by using a capacitor to store energy which can be used to accelerate the rate at which an electro-mechanical solenoid returns to its initial position.
2. Description of the Related Art
A wide range of pumps have been developed for displacing fluids under pressure produced by electrical drives. For example, in certain fuel injection systems, fuel is displaced via a reciprocating pump assembly which is driven by electric current supplied from a source, typically a vehicle electrical system. In one fuel pump design of this type, a reluctance gap coil is positioned in a solenoid housing, and an armature is mounted movably within the housing and secured to a guide tube. The solenoid coil may be energized to force displacement of the armature toward the reluctance gap in a magnetic circuit defined around the solenoid coil. The guide tube moves with the armature, entering and withdrawing from a pump section. By reciprocal movement of the guide tube into and out of the pump section, fluid is drawn into the pump section and expressed from the pump section during operation.
In pumps of the type described above, the armature and guide tube are typically returned to their original position under the influence of one or more biasing springs. Where a fuel injection nozzle is connected to the pump, an additional biasing spring may be used to return the injection nozzle to its original position. Upon interruption of energizing current to the coil, the combination of biasing springs then forces the entire movable assembly to its original position. The cycle time of the resulting device is the sum of the time required for the pressurization stroke during energization of the solenoid coil, and the time required for returning the armature and guide to the original position for the next pressure stroke. Engine speed is generally a function of the flow rate of fuel to the combustion chamber. Increasing the speed of the engine shortens the duration of each combustion cycle. Thus, a fuel delivery system must provide the desired volumes of fuel for each combustion cycle at increasingly faster rates if the engine speed is to be increased.
Where such pumps are employed in demanding applications, such as for supplying fuel to combustion chambers of an internal combustion engine, cycle times can be extremely rapid. Cycle time refers to the amount of time required for a fuel injector to load with fuel, discharge the fuel into the combustion chamber and then return to its original position to start the cycle over again. Cycle time is typically short for fuel injectors. For example, injectors used in a direct injection system can obtain a cycle time of 0.01 seconds. That equates to the injectors being able to load with fuel, discharge the fuel into the combustion chamber, and then prepare to reload for a subsequent cycle 100 times in a single second. While this cycle time seems very short, it is often desirable to reduce this time even further when possible.
Moreover, repeatability and precision in beginning and ending of pump stroke cycles can be important in optimizing the performance of the engine under varying operating conditions. While the cycle time may be reduced by providing stronger springs for returning the reciprocating assembly to the initial position, such springs have the adverse effect of opposing forces exerted on the reciprocating assembly by energization of the solenoid. Such forces must therefore be overcome by correspondingly increased forces created during energization of the solenoid. At some point, however, increased current levels required for such forces become undesirable due to the limits of the electrical components, and additional heating produced by electrical losses.
There is a need, therefore, for an improved technique for pumping fluids in a linearly reciprocating fluid pump. There is a particular need for an improved technique for providing rapid cycle times in fluid pumps, such as fuel pumps without substantially increasing the forces and current demands of electrical driving components.
The present invention provides a novel technique for pumping fluids in a reciprocating pump arrangement designed to respond to these needs. The technique is particularly well suited for use in fuel delivery systems, such as in chamber fuel injection. However, the technique is in no way limited to such applications, and may be employed in a wide range of technical fields. The pumping drive system offers significant advantages over known arrangements, including a reduction in cycle times and so forth.
The technique is based upon a drive system employing at least one permanent magnet and at least one coil assembly. The coil assembly is energized cyclically by a reciprocating circuit to produce reciprocating motion of a drive member, which may be coupled directly to the coil. The drive member may extend into a pumping section, and cause variations in fluid pressure by intrusion into and withdrawal from the pumping section during its reciprocal movement. Valves, such as check valves, within the pumping section are actuated by the variations in pressure, permitting fluid to be drawn into the pumping section and expressed therefrom.
More specifically, the drive section has a reciprocating coil assembly to which alternating polarity control signals are applied by a reciprocating circuit. A permanent magnet structure of the drive section creates a magnetic flux field which interacts with an electromagnetic field produced during application of the control signals to the coil. Depending upon the polarity of the control signals applied to the coil, the coil is driven in one of two directions of movement. The reciprocating circuit employs a storage capacitor and several switches to capture the energy of the reciprocating coil as the pump is driven downwardly. The charge is recycled as the capacitor dissipates, thereby reversing the polarity of the current through the coil and driving the coil assembly upwardly to its initial position. A drive member transfers movement of the coil to a pump element which reciprocates with the coil to draw fluid into a pump chamber and expel the fluid during each pump cycle.